During hydrocarbon exploration and production processes, it is common for the interiors of fluid conduits, including pipelines, wellbores, risers and umbilicals to become fouled. The fouling often leads to the formation of a blockage within the fluid conduit, which may be as a result of a gradual build-up of material on the inside surface of the conduit or the formation of a plug as an unwanted by-product of a (possibly unanticipated) chemical reaction. The blockage prevents further use of the fluid conduit and must be removed before the process can continue.
A range of techniques have been developed for removing blockages from fluid conduits. These range from lance or nozzle jet systems, which are inherently limited in their range, and ultrasonic systems which apply acoustic energy to the fluid to attempt to induce cavitation in the fluid.
It has also been proposed to use pulses of pressurised fluid in order to remove material from internal surfaces of fluid conduits and vessels. U.S. Pat. No. 5,183,513 describes a system in which a high pressure pump is coupled to a fluid vessel via a pressure regulator. A controllable valve is located in the fluid line between the vessel and the pressure regulator, and is connected to the vessel via a controllable valve. The valve is cyclically opened and closed to allow pressure pulses to pass into the vessel. The operation of the valve is controlled such that the pulses are formed at frequencies, pressures and temperatures that induce cavitation within the fluid which is said to remove material from the internal surfaces of the vessel.
Cavitation is undesirable in many applications because the implosion of bubbles can pit or damage the internal surfaces of a fluid system.
Pressure pulse systems such as those described in U.S. Pat. No. 5,183,518 are deficient in controlling the magnitude of the pulses. This presents a particular difficulty when the fluid conduit or vessel is sensitive to pressure, as may be the case in many hydrocarbon production and transportation installations. There is a concern amongst operators of such installations that uncontrolled pulses which are allowed to pass into a fluid system will cause damage resulting in reduced integrity and a shortened operating lifetime.
There is therefore a need for a method and apparatus for cleaning pipeline systems which is improved with respect to the previously proposed systems.
It is amongst the aims and objects of the invention to provide a method and apparatus for cleaning of fluid conduits or vessels which allows the delivery of fluid pressure pulses with controlled pressure pulses.
Further aims and objects will become apparent from reading the following description.